Yes metal, no wobble or sideways movement, no faffing about. Only moves in the way it needs to.
Leather curving around is OK as long as it’s tight and doesn’t let the clappers move about sideways. Leather can stretch over time though so you need to keep an eye on that.
[added:]
Here’s an image of the (more recent) bellows that belongs to my little D set, the hinge on my older bellows for the C set is the same type:
…where to start. I am very thankful for all the response!..
to JR - in my case the dead movement was not the due to inefficient valves (the repair from maker didn’t help) - it was just the fact that gusset shape was not the best combo with clappers shape, IMHO…
to rorybbellows - nice photo Rory, but Donohue bellows are mybe a bit to adventurous for my classic taste. But he makes most interesting inlet valves. I saw your black bellows with tall inlet valve - how can make them in such artistic shapes? Any idea?
to Tom_S - Michael Dow bellows suggestion comes out lots of times and they do sound mighty solution. But I need metal parts to be in silver color and I like to see some wood. Also some players I know replaced them with smaller bellows so, I gues it is matter of taste…
to Glenarley - thanks Glen for sharing your thoughts - I get your point. I agree it is much nicer to see long smoth use of bellows instead of quick action… I might send inquiry to Murray to check things…
to billh - thanks Bill for sharing your experience. I’ll check Kellehers…
to elbowmusic - nice video Nate. I gues the Kelleher gear is realy good…
to pancelticpiper - I know it sounds weird, but it is truth am talking to you. All 3 bellows were made by well known makers, not Pakistani stuff. Mybe I just had bad luck 
The leaking bellows were only few years old when I bought them and the air was already escaping through the surface of gusset - I gues it was single layer design. The noise on 2nd bellows was due to fold of leather gusset at the narrow point near the hinge - the leather was rubbing with opposite half and with wood and sometimes also wood with wood - it was designed like old belloows (2 holes and cord). And the inneficient example was as I already said due to not ideal geometry of gusset and/or clapper combination. When I started to close them, first 2,5 Inches were just lost and then it started to push air out. One of the bellows (the nicest looking one) had two of the mentioned issues at once…
to Mr. Gumby - can you recommend someone who can make me good metal hinged example, since Geoff is closed for orders?
to anyone
Where can I find some different photos of Thomson bellows like Calum is playing them in the video Glen shared ? Any website, photo gallery ?
Whats the difference between Kelleher and Thomson when playing? Pros and cons?
I repeat myself, Thank you gentlemen.
Joe Kennedy makes really nice metal hinged bellows. his email: unionpipemaker@yahoo.ca
Thanks for info. I saw few photos - they are gorgeous. I read somewhere that he makes them in union style and a bit smaller. Can they support full D set or better for flat sets?
I can attest that there’s lots of not great bellows out there. Most are serviceable, sure, but many are uncomfortable and inefficient. I have to say I’m surprised to hear someone say they haven’t ever seen bellows with any of those problems…
I have a Joe Kennedy full B set, an antique D narrow-bore set, as well as a regular D 3/4 set from a few makers - I have three different Kennedy bellows for these sets, but could use the same for all three - one of the bellows is in the old style with leather cord for the hinge, but the other two are metal hinges. I actually liked the non-metal hinged bellows better for a long while (which was also the first), as it fit my body better when I first got it. But now I use a metal hinged bellows for the first two sets. None of the bellows are particularly large, which I prefer, and they work just fine for all the sets. Note that the bags aren’t large either, which I also prefer.
Putting in another plug for Thompson bellows, small but so efficient, and drive a full set easily. I have had larger bellows, but I don’t like them nearly as much because there was more slack/delayed response with them. To paraphrase, bigger is not always better.
I forgot to ask, anyone knows if Derrick Gleeson can make same metal hinged bellows as Geoff Wooff? Thanks again